Structure of $\mathrm{Ag}(111)\mathrm{\text{−}}p(4\times 4)\mathrm{\text{−}}\mathrm{O}$: No Silver Oxide

The structure of the oxygen-induced $p(4\times 4)$ reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

Figure 1

Structural models of the $\mathrm{Ag}(111)\mathrm{\text{−}}p(4\times 4)\mathrm{\text{−}}\mathrm{O}$ structure (a) as proposed in Ref. 9 and (b) the current work. The ${\mathrm{Ag}}_9{\mathrm{O}}_6$ structure (referred to as “${\mathrm{Ag}}_{1.33}\mathrm{O}$” in Ref. 10) results from model (a) by removing the Ag adatoms marked by crosses.

Figure 2

STM images of the O-induced $p(4\times 4)$ structure on Ag(111). The insets show simulated images [25] at $V_{\mathrm{sample}}=-1\mathrm{V}$ for (a) the time-averaged atomic positions of an MD run and (b) the average density of the two equivalent orientations of the structure at 0 K. Small black circles mark the average positions of the Ag and O atoms, respectively. Frame (c) has been taken during reduction of the structure by CO.

Figure 3

(a) In-plane structure factors, (b) superstructure rods, and (c) crystal truncation rods of $\mathrm{Ag}(111)\mathrm{\text{−}}p(4\times 4)\mathrm{\text{−}}\mathrm{O}$. The error bars in (b) and (c) represent the combined statistical and systematical error. $L$ is given in reciprocal lattice units of an Ag(111) cell containing three atomic layers.

Figure 4

Photoemission spectrum of the Ag $3d_{5/2}$ level. The decomposition into different components is explained in the text.